Efficient and Mild Oxidation of Sulfides to Sulfoxides by Iodosobenzene Catalyzed by Cr(salen) Complex

Article abstract of DOI:10.1055/s-2003-42419

Cr(Salen) 1 is found to be an efficient catalyst for the oxidation of various sulfides to sulfoxides with iodosobenzene as terminal oxidant. Both aryl and alkyl sulfides are selectively converted into sulfoxides in excellent yields (>90%).

Full text of DOI:10.1055/s-2003-42419

SHORT PAPER
2461
Efficient and Mild Oxidation of Sulfides to Sulfoxides by Iodosobenzene
Catalyzed by Cr(salen) Complex
,
a
b
E
S
fficient
a
nd M
u
ild Oxidatio
n
n
of Sulfide
g
s
to Sulfoxides Soo Kim,* Gurusamy Rajagopal
a
Department of Chemistry and Center for Chemical Dynamics, Inha University, Incheon 402-751, South Korea
Fax +82(32)8675604; E-mail: sungsoo@inha.ac.kr
b
Department of Chemistry, Crescent Engineering College, Chennai, India
Received 5 June 2003; revised 28 August 2003
In recent years Cr(salen) complexes and hypervalent io-
Abstract: Cr(Salen) 1 is found to be an efficient catalyst for the ox-
idation of various sulfides to sulfoxides with iodosobenzene as ter-
minal oxidant. Both aryl and alkyl sulfides are selectively converted
into sulfoxides in excellent yields (>90%).
13
dine atoms have been employed to oxidize various or-
ganic substrates. To the best of our knowledge, there is no
report on the formation of sulfoxides by using Cr(salen)
complexes from a synthetic point of view. In continuation
of our interest in the oxidation studies by salen-type metal
complexes, we would like to report here an efficient and
selective oxidation of sulfides to sulfoxides utilizing 3,5-
disubstituted Cr(salen) (1, Figure 1)/PhIO.
Key words: sulfide, sulfoxide, Cr(salen), oxidation, selectivity
1
The selective and catalytic oxyfunctionalization is a piv-
otal reaction in organic synthesis that has received much
attention over the years. Transition metal complexes can
serve as excellent catalysts for various oxidative process-
es provided they are equipped with an appropriate organic
ligand. A large number of salen type metal complexes2
were used for numerous organic transformations. The se-
lective oxidation of organic sulfides to sulfoxides without
any overoxidation to sulfones is a challenging research in
synthetic organic chemistry because of the importance of
sulfides as intermediates in biologically active com-
Various sulfides were subject to oxidation under the sto-
ichiometric condition given in Table 1. Unsubstituted and
substituted thioanisoles (entries 1–4) underwent very
smooth oxidation with over 98% yield. The substituents
on the phenyl group showed no significant effect on reac-
tion time (entries 2–4). But nitro and cyano substituents
show little rate retardation due to their electron withdraw-
ing property (entries 5 and 6). Diphenyl sulfide underwent
clean oxidation to the corresponding sulfoxide with long-
er reaction time due to steric hindrance (entry 7). When
compared with PhIO/KBr1 system, our method requires
less reaction time for the oxidation of diphenyl sulfide and
gave a better yield. Further, the PhIO/KBr system shows
no or very little reaction with the substrates carrying elec-
tron-withdrawing substituents at the p-position.
3
4
5
6
pounds. Oxovanadium(IV), Mn(III), Ti(IV), and some
3d
7
highervalent chromium complexes have been widely
used as catalysts for oxidation of sulfides. Oxorheni-
8
um(V) dithiolates with tert-butyl hydroperoxide have
been reported as an oxidizing agent. The combination of
9
mercury(II) oxide/iodine serves as a good oxidizing
14
agent of sulfides. The role of hexafluoropropan-2-ol with
Such rate retardation has already been clearly observed
in the oxidation of diphenyl sulfide with longer reaction
time giving low yield. The insertion of a methylene group
into diphenyl sulfide reduced the steric hindrance as indi-
cated by a little shorter reaction time (entries 8 and 9).
Some linear dialkyl sulfides (entries 10–12) underwent
smooth oxidation very quickly (20–25 min) with excellent
yield. To test the activity of the present catalyst, a model
run was carried out with thioanisole without catalyst 1 and
was found that no sulfoxidation reaction had taken place
within the typical reaction time. The in situ formation of
1
0
H O for sulfoxidation has been reported in the litera-
2
2
1
1
ture. Photochemical oxidation of sulfides have been
studied. We have recently reported a mild and efficient
oxidation of sulfides with periodic acid catalyzed by
1
2
FeCl3.
N
O
N
O
+
(
salen)oxochromium(V) complex is responsible for the
Cr
Cl-
13a,15
sulfoxidation reaction.
state transfers oxygen to the substrate for the sulfoxidation
Scheme 1).
This hypervalent Cr(V)=O
(
N,N-Ethylenebis(3,5-di-tert-butylsalicylideneiminato)
chromium(III) chloride
Figure 1 Structure of the catalyst 1
SYNTHESIS 2003, No. 16, pp 2461–2463
x
x.
x
x
.
2
0
0
3
Advanced online publication: 07.10.2003
DOI: 10.1055/s-2003-42419; Art ID: F05103SS.pdf
Georg Thieme Verlag Stuttgart · New York
©

2
462
S. S. Kim, G. Rajagopal
SHORT PAPER
Table 1 Oxidation of Sulfides into Sulfoxidesa
IR (KBr): 2923, 1614, 1461, 1170, 836 cm–1.
Anal. Calcd for C H Cl CrN O (578.18): C, 66.49; H, 7.96; N,
O
S
3
2
46
2
2
4
.8. Found: C, 66.29; H, 7.8; N, 5.2.
(Salen)Cr(III)/PhIO
R1
R2
R1
R2
S
CH Cl r.t.
Oxidation of Sulfides to Sulfoxides with (Salen)Cr(III) (1)/
PhIO; General Procedure
2
2,
Entry Sulfide
Time
Yield of
Cr(salen) 1 (58 mg, 0.1 mmol) and sulfide (1 mmol) were dissolved
in CH Cl (3 mL) and the solution was stirred for 5 min. To this so-
R1
R2
Sulfoxide (%)b
2
2
lution was added PhIO (242 mg, 1.1 mmol) at once. The reaction
was monitored by TLC at regular intervals and continued for reac-
tion time mentioned in Table 1. After removal of the solvent, the
residue was purified by silica gel flash chromatography (EtOAc) to
afford the sulfoxide. All the sulfoxides thus obtained were identi-
fied by comparing NMR data with values reported in the
1
2
3
4
5
6
7
8
9
0
1
2
Ph
p-MeC H4
Me
Me
Me
Me
Me
Me
Ph
2 h
99
98
99
98
90
2.5 h
2.5 h
2.5h
4 h
6
6
p-BrC H4
1
4c,d,f
16
literature
and those of the authentic samples (Table 1).
p-ClC H4
6
p-NO C H
4
2
6
Acknowledgment
p-CNC H4
3.5h
91
6
The authors warmly thank Korea Research Foundation for the fi-
nancial support (KRF-2002-015-CP0203). Dr. G. Rajagopal is a
Brainpool Scientist assisited by a grant from KOFST and KOSEF,
Korea.
6 h (24 h)13d
91 (64)13d
Ph
PhCH2
PhCH2
Me(CH2)2
Me(CH2)3
Ph
3 h
98
94
96
95
94
PhCH2
2.5 h
References
1
1
Me(CH2)2
Me(CH2)3
20 min
20 min
25 min
(
1) Sheldon, R. A.; Kochi, J. K. Metal Catalyzed Oxidations of
Organic Compounds; Academic Press: New York, 1981.
2) (a) Noyori, R. Asymmetric Catalysis in Organic Synthesis;
Wiley: New York, 1994. (b) Ojima, I. Catalytic Asymmetric
Synthesis, 2nd ed.; VCH Publishers: Weinheim, 2002.
(
1
Me(CH2)
Me(CH2)7
7
a
Reagents and conditions: Cr(salen)(1)/PhIO/Sulfide/CH Cl = 0.1
2
2
(
c) Comprehensive Asymmetric Catalysis; Jacobsen, E. N.;
Pfaltz, A.; Yamamoto, H., Eds.; Springer Verlag: Berlin,
999. (d) Katsuki, T. Synlett 2003, 281. (e) Canali, L.;
mmol:1.1 mmol:1 mmol:3 mL.
b
Isolated yield.
1
Sherrington, D. C. Chem. Soc. Rev. 1999, 28, 85.
3) (a) Carreno, M. C. Chem. Rev. 1995, 95, 1217. (b) Sulfur
Centered Reactive Intermediates in Chemistry and Biology,
Nato ASI Series; Chatgilialoglu, C.; Asmus, K. D., Eds.;
Plenum: New York, 1990.
4) (a) Nakajima, K.; Kojima, K.; Kojima, M.; Fujita, J. Bull.
Chem. Soc. Jpn. 1990, 63, 2620. (b) Bolm, C. Coord. Chem.
Rev. 2003, 237, 245. (c) Pelotier, B.; Anson, M. S.;
Campbell, I. B.; Macdonald, S. J. F.; Prien, G.; Jackson, R.
F. W. Synlett 2002, 1055.
(
(
(
5) (a) Noda, K.; Husoya, H.; Yanai, K.; Irie, R.; Katsuki, T.
Tetrahedron Lett. 1994, 35, 1887. (b) Page, P. C. B.; Heer,
J. P.; Bethell, D.; Collington, E. W.; Andrews, D. M.
Tetrahedron Lett. 1994, 35, 9629. (c) Palucki, M.; Hanson,
P.; Jacobsen, E. N. Tetrahedron Lett. 1992, 33, 7111.
6) (a) Saito, B.; Katsuki, T. Tetrahedron Lett. 2001, 42, 3873.
Scheme 1
(
N,N -Ethylenebis(3,5-di-tert-butylsalicylideneiminato)chromi-
(
4
b) Tanaka, T.; Saito, B.; Katsuki, T. Tetrahedron Lett. 2002,
3, 3259.
um(III) Chloride (1)
1
3a
The new catalyst 1 was prepared analogous to the reported meth-
od for the unsubstitured catalyst. To a suspension of bis(3,5-di-tert-
butylsalicylidene)ethylenediamine (492 mg, 1 mmol) in THF (25
(
7) (a) Bharathy, J. B.; Ganesan, T. K.; Sheriff, A. I. A. M.;
Rajagopal, S. Tetrahedron 1997, 53, 1131. (b) Kannan, P.;
Sevvel, R.; Rajagopal, S.; Pichumanai, K.; Srinivasan, C.
Tetrahedron 1997, 53, 7635. (c) Ganesan, T. K.; Rajagopal,
S.; Bharathy, J. B. Tetrahedron 2000, 56, 5885. (d) Sevvel,
R.; Rajagopal, S.; Srinivasan, C.; Alhaji, N. I.; Chellamani,
A. J. Org. Chem. 2000, 65, 3334.
mL) was added a suspension of anhyd CrCl (246 mg, 1.2 mmol) in
2
THF (20 mL) with vigorous stirring under N at r.t. (ca. 20 °C) for
2
3
h. Then the dark brown solution was allowed to reflux in the pres-
ence of air for 3 h. The residue was suspended in H O (30 mL) and
2
the undissolved brown colored material was collected by filtration
(
8) Wang, Y.; Lente, G.; Espenson, J. H. Inorg. Chem. 2002, 41,
and washed with H O (3 × 10 mL). After filtration and concentra-
2
1
272.
tion of the filtrate with rotary evaporator, a brown material was pre-
cipitated on cooling overnight, which was collected and dried under
reduced pressure to afford the required complex 1; yield: 90%; mp
(
9) Orito, K.; Hatakeyama, T.; Takeo, M.; Suginome, H.
Synthesis 1995, 1357.
10) Ravikumar, K. S.; Zhang, Y. M.; Begue, J. P.; Delpon, D. B.
(
>300 °C.
Eur. J. Org. Chem. 1998, 63, 2937.
Synthesis 2003, No. 16, 2461–2463 © Thieme Stuttgart · New York

SHORT PAPER
Efficient and Mild Oxidation of Sulfides to Sulfoxides
2463
(
(
(
11) Zen, J. M.; Liou, S. L.; Kumar, A. S.; Hsia, M. S. Angew.
Chem. Int. Ed. 2003, 42, 577.
12) Kim, S. S.; Nehru, K.; Kim, S. S.; Kim, D. W.; Jung, H. C.
Synthesis 2002, 2484.
13) (a) Adam, W.; Gelalcha, F. G.; Saha-Moller, C. R.;
Stegmann, R. J. Org. Chem. 2000, 65, 1915. (b) Adam, W.;
Hajra, S.; Herderich, M.; Saha-Moller, C. R. Org. Lett. 2000,
(14) (a) Gasparrini, F.; Giovannoli, M.; Misiti, D. J. Org. Chem.
1990, 55, 1323. (b) Bonadies, F.; Angelis, F. D.; Locati, L.;
Scettri, A. Tetrahedron Lett. 1996, 37, 7129. (c) Ali, M. H.;
Stevens, W. C. Synthesis 1996, 764. (d) Ali, M. H.;
Bohnert, G. J. Synthesis 1998, 1238. (e) Hirano, M.;
Yakabe, S.; Itoh, S.; Clark, J. H.; Morimotoa, T. Synthesis
1997, 1161. (f) Ochiai, M.; Nakanishi, A.; Ito, T. J. Org.
Chem. 1997, 62, 4253.
2, 2773. (c) Daly, A. M.; Renehan, M. F.; Gilheany, D. G.
Org. Lett. 2001, 3, 663. (d) Tohma, H.; Maegawa, T.; Kita,
Y. Arkivoc 2003, Part vi, 62; http://arkat-usa.org/ark/
Journal/2003/Varvoglis/AV-667A/667.pdf.
(15) Samsel, E. G.; Srinivasan, K.; Kochi, J. K. J. Am. Chem. Soc.
1985, 107, 7606.
(16) Pouchert, C. J.; Behnke, J. The Aldrich Library of C and H
FT NMR Spectra, 1st ed., Vol. 2; Aldrich: Milwaukee, 1993.
1
3
1
Synthesis 2003, No. 16, 2461–2463 © Thieme Stuttgart · New York